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Length-to-Width Ratio
In stones with shapes other than round (such as marquise, pear, hearts, etc.), the length-to-width ratio is the relationship between the length of its shorter and longer dimensions.
Loupe
A loupe is a small magnifying glass used to view gemstones. Usually 10x, or ten-power, magnification. The FTC requires all diamond grading be done under 10-power magnification; any flaws not detected under this magnification are considered to be non-existent.
Luster
Luster is the most important factor in the beauty of a pearl. Luster is caused by light traveling down through layers of
nacre
and reflecting back to the eye from within the pearl, so a pearl’s luster depends on the nacre’s translucence and the arrangement of its overlapping plates.